The present invention relates generally to pipe bending machines, and is particularly concerned with a dual headed bending machine for forming a plurality of successive bends about different bend dies.
Conventional pipe bending machines typically have a fixed, elongate machine bed supporting a moving carriage assembly carrying a rotating chuck in which a pipe section to be bent is gripped. A rotatable bending head and clamp die are located at a forward end of the machine bed, and the carriage advances the pipe between the bending die and clamp die, a section of pipe is gripped between the dies, and the bending head is rotated about a vertical axis to draw the pipe around the die and form the bend. The dies are then retracted, and the pipe is advanced longitudinally to the next location where a bend is to be formed.
If closely adjacent bends are to be formed, the bend and clamp dies must be formed with cavities having a compound curvature specific to a given pair of adjacent bends. Different bend dies are also required where bends of different radius are to be formed. Thus, the bending operation must often be stopped for manual changing of one set of bend and clamp dies for another. These tooling changes are difficult and time consuming.
Other problems arise when multiple bends are formed in a pipe. For example, where several bends are to be formed, care must be taken to ensure that a previously bent pipe portion, which will extend forwardly from the bend die, will not interfere with the bend head or other parts of the machine when the next bend is formed. In the past, it has been the practice to change dies or select other bend dies when changing from a right-hand bend to a left-hand bend, which also considerably lengthens the bending process.
Dual headed pipe bending machines have been proposed in the past to reduce these problems. U.S. Pat. No. 4,313,324 of Pearson, assigned to Eaton-Leonard Corp., describes a bending machine having a bending head carrying first and second bend die assemblies positioned at opposite ends of a common, horizontal bend die shaft. The pipe holding carriage and track are pivotable through 180.degree. between bend axes defined on diametrically opposite, left and right positions of the machine bed so as to align the pipe with the respective bend die assemblies. Movement of the pipe back and forth between the two positions can be time-consuming.
In U.S. Pat. No. 4,843,859 of Togoshi, a dual headed pipe bender is described in which opposite left and right hand bending dies are mounted for rotation about spaced, vertically extending axes, and are supported on a support frame mounted on a carriage which is movable back and forth across the front end of the machine bed to move the bending dies in a direction transverse to the pipe axis, bringing a selected bending die into alignment with the pipe to be bent. The clamp die assemblies rotate in opposite directions to form right and left hand bends. This requires movement of the bend heads along a relatively long travel path between the two alignment positions, since a relatively large separation is required between the vertically oriented bend heads. Also, interference problems can arise when successive bends are formed by bending pipe along a vertical bend axis.
U.S. Pat. No. 5,499,522 of Schwarze describes a double-head pipe bending machine which has right and left hand bending heads positioned on opposite sides of the central axis of a machine bed, and the pipe holding carriage is supported on a slide which moves the carriage horizontally between the right and left hand bending heads. Each bend head is mounted for rotation about a vertical axis, with the right hand bend head performing right handed bending, and the left hand bend head performing left handed bending.
The Schwarze machine involves horizontal translation of a tube which is held at the carriage only, which may produce a cantilever effect and resultant alignment problems, particularly where a relatively long tube is to be bent. This arrangement also may cause interference problems where previously formed bends interfere with the bend head or other parts of the machine when subsequent bends are formed. Also, the pipe must be moved a relatively long distance to align with the respective bend heads, due to the separation required between two vertically oriented bend heads to avoid interference.